The present invention relates to an electric light bulb of the type presenting a longitudinal axis and having a longitudinal filament disposed at least approximately on said axis and suitable for emitting light when it is electrically powered, and a glass enclosing the filament and presenting around it at least for the most part an outer peripheral face that is at least approximately circularly cylindrical about the axis.
Bulbs of this type, a non-limiting example of which is constituted by shuttle-shaped xe2x80x9cfestoonxe2x80x9d bulbs, are generally circularly symmetrical about the axis and have two axial terminals for electrical connection to the filament at mutually opposite ends, and they emit light radially in all directions when the filament is powered with electricity. However, in numerous applications, it is pointless to emit light in some radial directions, so such bulbs are associated with a reflector or mirror which deflects the light emitted in this way to directions in which it is useful. This applies, for example, in applications of such bulbs to making lights for motor vehicles or indeed to making strip lights comprising a support in the form of a longitudinal strip together with a plurality of electric light bulbs of this type that are carried and held individually in longitudinal alignment by the support.
In such applications, the reflector or mirror is presently carried independently of the bulb, outside the bulb by a support which is nevertheless generally common, having the reflector or mirror generally secured thereto, and most often directly forming an integral portion thereof.
As a result, the average direction of light emission from the assembly constituted by the bulb and the reflector or mirror, whether by direct emission from the filament or by reflection of a portion of the light coming from the filament, is determined directly firstly by the shape of the reflector or mirror and by its positioning relative to the filament, and secondly by the orientation in which the support and with it the reflector are fixed to a counterpart which, for a vehicle light, is constituted by a piece of bodywork, and for a strip light is constituted by an element of a building front, an internal partition, or a wall of a piece of furniture, depending on what the strip light is used for.
This does not lead to any drawback in certain applications, such as vehicle signaling, given that in any event the support of the bulb and the reflector or mirror are generally integral portions of a light unit which is specially designed for each vehicle and which is suitable for enabling light to be emitted in directions that are determined once and for all relative to the vehicle. However, in other applications, such as making strip lights, directly securing or integrating the reflector or mirror to the support presents a drawback since the orientation in which the support is fixed determines the average direction in which light is emitted by the assembly constituted by the bulb(s) and the support. Unfortunately, it is sometimes difficult to reconcile the constraints on installing the support with desires or needs in terms of lighting; in addition, the average direction in which light is emitted, determined by the orientation of the support, is the same for all of the bulbs and there is no possibility of varying this average direction between zones that succeed one another longitudinally along the strip light, e.g. to emphasize certain items in relief on a building front; similarly, the light emitted in such conditions is in the form of a beam having a flare angle that is determined by the shape of the reflector or mirror, and, for example, it is not possible to increase this flare angle, whether only locally or over the entire length of the strip light.
The object of the present invention is to remedy those drawbacks and, to this end, in a first aspect, the present invention provides a bulb of the type specified in the introduction and characterized in that it further comprises, outside the glass, a mirror having a concave reflecting surface which is placed locally in contact with the glass and via which the mirror is directly secured to the outer peripheral face of the glass, which reflecting surface is defined by longitudinal generator lines and presents a cross-section different from the cross-section of the outer peripheral face of the glass, which section is selected and disposed relative to the axis in such a manner that the reflecting surface is tangential to the outer peripheral face of the glass along a common longitudinal generator line, and relative to the filament in such a manner that the reflecting surface concentrates the light emitted by the filament when it is electrically powered into a beam of predetermined orientation and flare angle.
Lamps are indeed already known in which the glass is metallized directly or carries a reflecting metal cap that is directly complementary to the glass, however the purpose is generally merely to prevent light from being emitted in certain directions, the lamp being otherwise associated with external optical means for shaping its emission of light into a beam of predetermined orientation and flare angle and in any event secured, sometimes adjustably, not to the bulb itself, but to a support for the bulb; that applies for example to certain bulbs used in projection apparatuses or indeed bulbs for indirect lighting devices. Under such circumstances, the metallization or the metal cap serves essentially as a mask and, although it makes it possible to avoid loss of light by reflecting the light emitted towards it from the filament of the bulb, it does not have a direct role in forming a beam. Bulbs are also known that contain an internal reflecting metal cup, and this applies for example to certain bulbs for motor vehicle headlights; in this case likewise, the idea is essentially to constitute a mask that prevents light being emitted in certain directions, and it is other means, in practice a reflector integrated in the bulb support or secured to said support, that serve to form the beam, generally in co-operation with portions in relief carried by a closure globe of the headlight.
In contrast, with a bulb of the present invention, it is the mirror that is secured directly to the glass of the bulb but that is shaped differently from said glass that determines the orientation and the flare angle of the beam.
Although a bulb of the invention can have other applications, this possibility is particularly advantageous when making strip lights that comprise a longitudinal support and a plurality of electric bulbs of the type specified in the introduction, and in a second aspect, the present invention extends to such strip lights insofar as at least one of said bulbs is a bulb of the invention.
Under such circumstances, the orientation and the flare angle of the beam are not determined, or at least not solely determined, by the orientation in which the support is installed, but can be selected at will, at least to a large extent, by choosing to use one or more bulbs of the present invention.
When in a preferred embodiment the support is suitable for carrying and holding individually at least one bulb of the invention in a plurality of orientations about its axis, which orientations are selected independently of the orientations of other bulbs around their axes, and this can be achieved by means of supports that are themselves known when the bulb of the invention is of the xe2x80x9cfestoonxe2x80x9d type. When a plurality of bulbs of the invention are used on a common support, it is possible to orient all of the bulbs in the same manner, thereby obtaining a uniform direction of light emission while benefiting from the advantage of being able to select this direction in a manner that is largely independent of the orientation in which the support is installed. Nevertheless, in such an embodiment, it is also possible to orient individually bulbs of the invention distributed along the strip, in which case it is possible for example to modulate the direction of lighting as a function of the portions in relief to be illuminated, by orienting a certain number of adjacent bulbs in one zone of the strip light identically while orienting the bulbs in another zone thereof differently; it is then also possible to vary the orientation of the bulbs along their common support in systematic manner and thus, for a given flare angle of the beam emitted by each bulb, to increase the flare angle of the beam emitted by the bulbs considered together; thus, in order to satisfy various requirements, there is no need to use bulbs of the invention having mirrors shaped so as to correspond to emitted beams having different flare angles.
This gives rise to a large increase in the options made available by strip lights in terms of being adaptable to requirements.
Nevertheless, the transverse size of a bulb of the invention is not greatly increased by the presence of the mirror, so it remains compatible with the components of previously known strip lights, i.e. it can be mounted thereon to replace conventional bulbs which do not have their own mirrors.
In conventional manner, a strip light of the invention, particularly when it is intended for use outside, can include a transparent longitudinal tube coaxially surrounding the bulbs together with the support and suitable for being, at will, closed in leakproof manner or opened, in particular for the purpose of changing bulbs.
Various mirror shapes and various mirror positions relative to the filament of the bulb can be envisaged, depending on requirements.
When a parallel beam of light is to be emitted, a bulb of the invention is characterized in that the cross-section of the reflecting surface is parabolic and tangential to the cross-section of the outer peripheral face of the glass, in that its focus lies on the axis, and in that its directrix is situated at a distance from the axis that is equal to the outside diameter of the glass.
However, it should be observed that the filament does not necessarily coincide with the axis; in particular, numerous xe2x80x9cfestoonxe2x80x9d-type bulbs have a filament that is wound helically around the axis so that even when the reflecting surface has a cross-section that is parabolic and accurately placed in the manner described above, the beam that is emitted by the assembly constituted by the bulb with its mirror when the filament is powered electrically will be only approximately parallel.
Thus, for a beam that provides a good approximation to being parallel, an acceptable embodiment of the bulb of the invention is characterized in that the cross-section of the reflecting surface is circular and tangential to the cross-section of the outer peripheral face of the glass, in that its center is placed on the outer cross-section of the glass, and in that its radius is equal to the outside diameter of the glass. This choice facilitates manufacture of the mirror considerably and consequently considerably facilitates manufacture of the bulb of the invention as a whole, since a mirror suitable for this embodiment can be obtained by a curving operation that is particularly simple to implement, starting from a sheet of suitable material, e.g. aluminum or stainless steel; naturally, such implementation of the mirror by curving a sheet can be adopted for a mirror having a different cross-section.
Preferably, the cross-section of the reflecting surface is symmetrical about a plane containing the axis, and/or the reflecting surface extends over an angle relative to the axis that is not greater than 180xc2x0, and that is preferably close to 180xc2x0, in such a manner respectively as to enable the bulb to be installed either way round on its support, particularly when the bulb forms part of a strip light, and to be able to benefit from a degree of directionality in the illumination obtained; nevertheless, it would not go beyond the present invention to give the reflecting surface shapes that are different.
The way in which the mirror is secured to the glass of the bulb can also be selected freely, providing it simultaneously preserves the reflecting power of the reflecting surface and withstands the operating temperatures of the bulb.
Preferably, the mirror is stuck to the outer peripheral face of the glass via its reflecting surface by means of adhesive that is transparent or translucent, and good results have been obtained in testing with a xe2x80x9cfestoonxe2x80x9d-type bulb using a commercially available adhesive that is polymerizable by being exposed to ultraviolet radiation. This example is not limiting in any way, and in particular with bulbs that operate at higher temperatures the person skilled in the art is in a position to make the most appropriate selection for each circumstance; specifically, good results have been obtained during testing with a ceramic adhesive for use with halogen bulbs.